The present invention generally relates to extracorporeal sensing modules for use in monitoring parameters of body fluids, and more particularly to an extracorporeal sensing module that has an internal surface that is a smooth and isodiametric cylinder throughout its length, which smooth internal surface continuously incorporates the surface of each electrode of the extracorporeal sensing module.
In instances of critical illness as well as critical surgical procedures such as open heart surgery, it is often mandatory to continuously monitor certain parameters of body fluids such as blood, this monitoring being with regard to temperatures, concentrations of various ions, concentrations of gases as well as concentrations of other components. In other less critical instances, such as dialysis, such monitoring is desirable. One approach for determining these types of parameters is to simply withdraw samples of the body fluid such as blood from the patient and to analyze same in vitro for ion and gas concentrations, for example. The results of such analytical procedures provide discrete information, and unless samples are taken with sufficient frequency, the results of such in vitro analyses might fail to timely indicate a trend. From a practical standpoint, there are limitations on the frequency of such in vitro sampling as generally dictated by the patient's status. Still further, the physician needs accurate and timely data, preferably continuous data, with regard to the development of any adverse or detrimental trends.
In vivo monitoring devices have been suggested and are available to monitor various parameters on a continuous basis. These devices include transcutaneous blood gas monitors such as those for measurement of oxygen or carbon dioxide tensions. Other devices have been designed to provide for direct measurement of ions, gases and other components of body fluids, such devices including an extracorporeal sensor module having a sensor protruding into the flow path of blood traversing a length of tubing. Devices of this type are often used, for example, to measure the concentration of potassium ions electrochemically, the potassium ion sensors being based on coated wire techniques with ion concentration being determined by potentiometric analysis.
Measurement of potassium, sodium, calcium and chloride ion concentrations are important in connection with many treatments and monitoring situations. For example, the potassium gradient is the principal contributor to normal functioning of all nervous and muscular tissue, especially the tissue of the heart. In the treatment of burns, diabetes, postcardiopulmonary by-pass, acute myocardial infarction as well as other intensive care conditions, the continuous measurement of potassium ion concentration is extremely important. Because of this importance, the description of the present invention will be directed primarily to the monitoring of potassium ion concentration while it will be understood that the sensing module of the present invention may also be used for monitoring of body fluids for other purposes, including but not limited to monitoring the concentration of other ions, gases or components.
Devices designed to date for in vivo monitoring have exhibited a common failing. Inadequate recognition of the importance of maintaining laminar flow of blood, for example, through the sensing module has prevailed. Projection of the sensor into the path of blood flow results in turbulence. The turbulent flow of blood increases the risk of entrapment of air bubbles, increases the likelihood of protein denaturation and can cause cell damage, each with its attendant problems. Cell damage can cause the cell contents to be released into the blood resulting in a higher concentration of the component, for example potassium ions, being measured than would exist in the blood without cell leakage. This detrimental result can be of major significance during surgery and treatment of critical conditions of the type referred to hereinabove. Additionally, turbulent flow of blood can result in clot formation.
Accordingly, there is a need for an improved extracorporeal sensing module for monitoring the parameters of body fluids. A general object of the subject invention is to provide such a module which is capable of establishing and maintaining laminar flow of body fluids therethrough while effectively analyzing or monitoring such body fluids.
Another object of this invention is to provide an extracorporeal flow cell or module which is of uncomplicated design and manufacture and in which the surface of the wall of the fluid flow passage is mutually defined by the module housing and by the sensing and reference electrode assemblies, thereby preventing the creation of turbulence by avoiding any projection of the sensor electrode assembly and/or reference electrode assembly into the path of fluid flow.
Still another object of the present invention is to provide an improved extracorporeal sensing module which provides an isodiametric fluid flow using sensor and/or reference electrode assemblies with confluent areas.